This application claims priority to Korean Patent Application No. 2003-0080100, filed on Nov. 13, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates generally to pickup actuators for disc drives such as optical pickup actuators, and more particularly to a pickup actuator having effective coil portions for high sensitivity.
2. Description of the Related Art
An optical pickup records and/or reproduces information on/from an optical disc within an optical disc drive. The optical pickup moves in a radial direction over the optical disc that is an optical information storage medium during such recording/reproducing.
A pickup actuator moves an objective lens of the optical pickup in tracking, focus, and/or tilt directions such that a light beam is focused on a desired spot of the optical disc. The tracking direction refers to the radial direction of the optical disc such that a light beam spot is formed at the center of a track of the optical disc. The focus direction refers to upward/downward from the optical disc for directing the light beam onto the optical disc with desired focus.
Recently, a numerical aperture (NA) of the objective lens has increased and a wavelength of the light beam has decreased for high-density optical storage devices. Such increased numerical aperture and such decreased wavelength decrease a tilt margin of the pickup actuator. Thus, the pickup actuator is desired to perform three-axis control including in a tilt direction as well as the tracking and focus directions. Such a pickup actuator is referred to as a tilt driving optical pickup actuator.
FIG. 1 shows a perspective view of an example conventional tilt driving optical pickup actuator. Referring to FIG. 1, the conventional tilt driving optical pickup actuator includes a bobbin 2 having an objective lens 1 mounted thereon, a plurality of wires 6, and a magnetic circuit that is formed at four sides of the bobbin 2 for moving the bobbin 2.
One end of each wire 6 is attached to the bobbin 2 and the other end of each wire 6 is fixed to a holder 3 mounted on a base 5. With suspension from such wires 6, the bobbin 2 is movable in the focus direction F, the tracking (i.e., radial) direction T, and a radial tilt direction RT with respect to the base 5.
A respective pair of the wires 6 may carry current for driving in each of the focus and tracking directions. In FIG. 1, wires used to carry current for driving in the tilt direction are not shown.
The conventional magnetic circuit of FIG. 1 includes a focus coil 4 wound around the bobbin 2 for moving the objective lens 1 in the focus direction F. In addition, two pairs of tracking coils 7a and 7b are disposed on the two sides of the bobbin 2 that are parallel along the tracking direction. Furthermore, each of a pair of tilt coils 9a and 9b is disposed on one of the remaining two sides of the bobbin 2.
The conventional magnetic circuit of FIG. 1 also includes magnets 10 and 11 and yokes 14, 15, and 16 at the four sides of the bobbin 2. When currents flows through the focus coil 4, the tracking coils 7a and 7b, and/or the tilt coils 9a and 9b, electromagnetic forces are generated for moving the bobbin 2 and thus the objective lens 1.
First magnets 10 are disposed on first yokes 14 for driving the bobbin 2 in the focus and tracking directions. Second magnets 11 are disposed on second yokes 16 for driving the bobbin 2 in the tilt direction. Third yokes 15 are internal yokes while first and second yokes 14 and 16 are external yokes that direct magnetic fields used for driving in the focus, tracking, and tilt directions.
Further referring to FIG. 1, when current flows through the focus coil 4, an electromagnetic force is exerted on the focus coil 4 from interaction of such current with the magnetic field of the magnets 10 to move the bobbin 2 and thus the objective lens 1 in the focus direction F. When current flows through the tracking coils 7a and 7b, an electromagnetic force is exerted on the tracking coils 7a and 7b from interaction of such current with the magnetic field of the magnets 10 to move the bobbin 2 and thus the objective lens 1 in the tracking (i.e., radial) direction T.
When current flows through the tilt coils 9a and 9b, an electromagnetic force is exerted on the tilt coils 7a and 7b from interaction of such current with the magnetic field of the magnets 11. When currents flow through the tilt coils 9a and 9b in different directions such that oppositely directed electromagnetic forces are exerted on the tilt coils 7a and 7b, the bobbin 2 and thus the objective lens 1 are moved in the radial tilt direction RT.
In the conventional optical pickup actuator of FIG. 1, one side of each tracking coil 7a or 7b forms an effective coil portion on which electromagnetic force in generated, resulting in low efficiency and sensitivity of control in the tracking direction T. Additionally in the conventional optical pickup actuator, magnets are disposed on all four sides of the bobbin 2 resulting in higher cost and complexity of manufacture.
Generally, a pickup actuator for a disc drive is desired to have high control sensitivity and low cost and complexity of manufacture.